M270M Gr.345W पूर्वतापन — H16, Low HI, 20–40 mm: 250°F

M270M Gr.345W / M270 Gr.50W

AASHTO M270M Gr.345W (M270 Gr.50W) is a weathering bridge steel with 345 MPa (50 ksi) yield that forms a protective oxide patina for unpainted bridge service. The copper-chromium-nickel alloying provides atmospheric corrosion resistance, eliminating lifetime repainting costs estimated at $15–25 per square foot per cycle. Weld filler must match the weathering composition (E8018-W2 or equivalent) for exposed joints. NFC preheat per Table 6.3 Group 1; FC per Tables 12.6/12.7 which carry higher preheat than the non-weathering grades.

M270M Gr.345W / M270 Gr.50W के लिए FC पूर्वतापन को समझना

Weathering 345 MPa (50 ksi) bridge steel for unpainted service. Under D1.5 fracture-critical requirements (Clause 12), the combination of H16 hydrogen designation and this heat input band requires 250°F minimum preheat at 20–40 mm (3/4–1½ in). Lower hydrogen levels (H4 < H8 < H16) allow lower preheat because less hydrogen enters the weld deposit. Similarly, higher heat input reduces preheat requirements because slower cooling rates give hydrogen more time to diffuse out.

M270M Gr.345W / M270 Gr.50W कहाँ उपयोग होता है

Deployed in unpainted bridge plate girders across humid, coastal, and high-maintenance-cost environments. The weathering patina eliminates lifetime repainting cycles estimated at $15–25/sq ft per cycle. Weld filler must match the weathering composition (E8018-W2 or ER80S-G-W) for exposed joints to ensure the weld face develops the same protective oxide as the base metal. Conventional Gr.345W is being replaced by HPS345W in new designs due to superior weldability.

M270M Gr.345W / M270 Gr.50W के लिए H16 हाइड्रोजन नियंत्रण

Weathering Gr.345W (50W) at H16 is used for field splices when self-shielded FCAW is the only practical process due to wind exposure on elevated bridge erection. The significantly higher preheat at H16 — often 40–60°F above H4 — makes weather-window scheduling critical for winter field splice operations.

20–40 mm (3/4–1½ in) पर पूर्वतापन क्यों महत्वपूर्ण है

Material from 20 to 40 mm (3/4 to 1-1/2 in) includes many girder web plates, splice plates, and bearing stiffener plates. Preheat increases to 20°C (70°F) for Group 1 and 50°C (125°F) for Group 2 under Table 6.3. The thicker section slows hydrogen diffusion, requiring higher preheat to maintain safe cooling rates.

20–40 mm (3/4–1½ in) पर M270M Gr.345W / M270 Gr.50W

At 20–40 mm, Gr.345W (50W) serves as the primary plate for unpainted bridge girder webs and connection plates. Weathering steel butt splices require the same CJP quality as painted Gr.345 but with compositional matching of the filler metal. Improper filler selection leaves a cosmetically distinct weld face that does not develop the same protective oxide, creating a maintenance concern on exposed bridges.

H16 पदनाम पर अधिक पूर्वतापन

H16 उपभोज्य प्रति 100g में 16 mL तक विसरणशील हाइड्रोजन की अनुमति देते हैं — FC पुल वेल्डिंग के लिए अनुमत उच्चतम स्तर। 1.2–2.0 kJ/mm ऊष्मा इनपुट के साथ 20–40 mm (3/4–1½ in) पर, 250°F (120°C) पूर्वतापन उच्च हाइड्रोजन क्षमता की भरपाई करता है। H8 या H4 उपभोज्य पर स्विच करने से इस जोड़ के लिए आवश्यक पूर्वतापन कम होगा।

H16 1.2–2.0 kJ/mm · 20–40 mm (3/4–1½ in) पर अन्य पुल स्टील

H16 1.2–2.0 kJ/mm पर M270M Gr.345W / M270 Gr.50W

विभिन्न संयोजन आज़माएँ

किसी भी AASHTO M270 स्टील, हाइड्रोजन स्तर, और ऊष्मा इनपुट संयोजन को देखने के लिए D1.5 ब्रिज पूर्वतापन कैलकुलेटर का उपयोग करें। स्ट्रक्चरल स्टील के लिए D1.1 पूर्वतापन कैलकुलेटर भी देखें।

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